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Snowmelt + Rain Probable Max Rain 380,000 417,000 29,060,000 2,063,600 Apr-July 6 days The peak and volume of the probable maximum rain flood were recomn\ended for use as were the maximum volumes for the probable maximum snowmelt and spring floods. However, the peaks for the latter two floods were not adopted, since they were lower than the peak discharges experienced with the 1884 and 1921 floods. The study recommended revising the peak discharge estimates. 3. Inflow Desiqn Flood Study, Glen Canyon Dam Site, Colorado River above Lees Ferry, Arizona, June 1954, by A.M. Gering. This 1954 investigation revised the 1951 studies, but built upon many of the results. The snowmelt flood volume of 28,500,000 acre- feet developed in the 1951 study was retained. The drainage basin above Glen Canyon was divided into the Green River, the Colorado River, and the San Juan River basins. Correlations between accumulated April-July runoff and accumulated maximum temperatures were used to shape the snow flood hydrograph. The volume was prorated to develop hydrographs for each basin. The hydrographs were added together and combined with a spring-type rain flood. The inflow design floods that were recommended for use in the design of the Glen Canyon Dam spillways are shown in table 1.6 and on figure 1.3. Table 1.6.--1954 Glen Canyon inflow design flood Peak Volume Flood Event (ft3/s) (acre-feet) Duration Historic snowmelt season runoff was analyzed on a probability of occurrence basis to evaluate the diversion requirement flows for construction of Glen Canyon Dam. Diversion requirement hydrographs were developed, and the results are presented on table 1.7. 4. Review of Inflow Desiqn Flood Study - Glen Canyon Dam Site - Colorado River Storage Project, April 5, 1955, by D. L. Miller. The design floods developed in the June 1954 study were approved for use, as were the diversion requirement flood hydrographs. Recommendations on routing the inflow design flood through Glen Canyon Dam and Reservoir were also made as part of the review. The reservoir was assumed to be at the top of the conservation pool, elevation 3700 feet (26,000,000 acre-feet), during the onset of the probable maximum rain flood. For the snowmelt plus rain event, the reservoir was assumed to contain 22,500,000 acre-feet of storage (elevation 3685 feet). Operations were based on runoff forecasts and an integrated criteria for operating Colorado River basin reservoirs. 13